As a partial government shutdown approaches its two-week point, concerns are growing that a heavily impacted Internal Revenue Service will delay issuing taxpayers' refunds.

The agency has categorized issuing tax refunds as a "non-excepted" activity — meaning those tasked with processing refunds would be furloughed during a shutdown. Meanwhile, several types of tax return processing were deemed "Necessary for the Safety of Human Life or Protection of Government Property."

That's according to a December shutdown plan that lays out the first five business days of the agency's response during a shutdown occurring outside of tax season. While the document notes the plan can be reassessed and furloughed employees can be recalled, The Wall Street Journal reported Wednesday and CNN reported Thursday that the IRS generally does not issue refunds during a shutdown.

The IRS plan says that only 12.5 percent of the IRS workforce is authorized to work during a shutdown, while the rest of the agency faces furloughs.

That plan might be revised as soon as Friday, as the agency shifts into tax season, which typically starts in mid-January, CNN reports, citing a source familiar with the matter.

As budget negotiations to reopen the government have stalled over President Donald Trump's demand for funding to build a border wall, the risk is growing that tax refunds could be delayed if furloughed IRS workers don't return to work.

A delay in tax refunds is likely to disproportionately affect low-income Americans, The Wall Street Journal reports. With little or no income-tax liability, these taxpayers often use a sizable refund to help pay down debt, the publication says.

People try to cross the river Munhinga by bypassing a damaged bridge after the passage of the cyclone Idai in Mozambique, March 21, 2019. Mozambican President Filipe Nyusi issued a national emergency decree on Tuesday and said 350,000 people were 'at risk.' ANDRE CATUEIRA, EPA-EFE

A woman flashes the victory sign in front of a bonfire as Turkish Kurds gather during Newroz celebrations for the new year in Diyarbakir, Turkey, on March 21, 2019. Newroz is an ancient Persian festival, which is also celebrated by Kurdish people, marking the first day of spring, which falls on March 21. ILYAS AKENGIN, AFP/Getty Images

U.S. ambassador in Germany Richard Grenell, center back ground, welcomes soldiers from the 1st Armored Division, based in Fort Bliss, Texas, at Tegel airport in Berlin, Germany, March 21, 2019. Over three hundred soldiers have arrived in Germany from their base in Texas in the first test of a new American strategy to rapidly deploy troops based in the United States to Europe to bolster the NATO deterrent against possible Russian aggression. Dorothee Thiesing, AP

Fishermen sort their nets next to the 37-meter-long 'KAWS:HOLIDAY' 'Companion' inflatable sculpture in Hong Kong, China on March 21, 2019. KAWS:HOLIDAY, made by US artist and designer Brian Donnelly known professionally as Kaws, will be displayed in Hong Kong's Victoria Harbour from March 22 to 31, 2019. JEROME FAVRE, EPA-EFE

An Indian raveller is doused with colored water during Holi festival celebrations in Chennai, India on March 21, 2019. Holi, the popular Hindu spring festival of colors is observed in India and across countries at the end of the winter season on the last full moon of the lunar month. ARUN SANKAR, AFP/Getty Images

A model presents a creation from the Autumn/Winter 2019 collection by South Korean designer Chanu for the label 'ACUOD by CHANU' during the Tokyo Fashion Week in Tokyo, Japan on March 21, 2019. FRANCK ROBICHON, EPA-EFE